UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): February 6, 2015

ONCOTHYREON INC.

(Exact name of registrant as specified in its charter)

2601 Fourth Avenue, Suite 500

Seattle, Washington 98121

(Address of principal executive offices, including zip code)

(206) 801-2100

(Registrant’s telephone number, including area code)

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

Item 1.01 Entry into a Material Definitive Agreement.

Underwriting Agreements

On February 6, 2015, Oncothyreon Inc. (the “Company”) entered into two underwriting agreements (each, an “Underwriting Agreement”) with Jefferies LLC, as underwriter, (the “Underwriter”) for separate but concurrent offerings of the Company’s securities, which together are expected to result in gross proceeds to the Company of approximately $22.2 million.

The first Underwriting Agreement relates to the public offering and sale of 13,500,000 shares of the Company’s Common Stock, at a price to the public of $1.50 per share (the “Common Stock Offering”). Pursuant to the first Underwriting Agreement, the Underwriter has agreed to purchase these securities from the Company at a price of $1.41 per share. As part of the Common Stock Offering, the Company also granted the Underwriter a 30-day option to purchase 2,025,000 additional shares of the Company’s Common Stock.

The second Underwriting Agreement relates to the public offering and sale of 1,333 shares of the Company’s Series B Convertible Preferred Stock (the “Series B Offering”). The offering price to the public is $1,500.00 per share of Series B Convertible Preferred Stock. Pursuant to the second Underwriting Agreement, the Underwriter has agreed to purchase these securities from the Company at a price of $1,410.00 per share.

The rights, preferences and privileges of the Series B Convertible Preferred Stock are set forth in a Certificate of Designation of Preferences, Rights and Limitations of Series B Convertible Preferred Stock, which the Company expects to file with the Delaware Secretary of State on or before February 11, 2015. Each share of Series B Convertible Preferred Stock is convertible into 1,000 shares of the Company’s Common Stock at any time at the holder’s option. The holder, however, will be prohibited from converting Series B Convertible Preferred Stock into shares of common stock if, as a result of such conversion, the holder, together with its affiliates, would own more than 4.99% of the shares of the Company’s Common Stock then issued and outstanding, which percentage may be increased at the holders’ election up to 19.99% upon 61 days’ notice to the Company. In the event of the Company’s liquidation, dissolution, or winding up, holders of Series B Convertible Preferred Stock will receive a payment equal to $0.0001 per share of Series B Convertible Preferred Stock before any proceeds are distributed to holders of Common Stock, pari passu with any distribution of proceeds to holders of Series A Convertible Preferred Stock and after any distribution of proceeds to holders of Class UA Preferred Stock. Shares of Series B Convertible Preferred Stock will generally have no voting rights, except as required by law and except that the consent of holders of a majority of the outstanding Series B Convertible Preferred Stock will be required to amend the terms of the Series B Convertible Preferred Stock. Shares of Series B Convertible Preferred Stock will not be entitled to receive any dividends, unless and until specifically declared by the Company’s board of directors, and will rank:

in each case, as to distributions of assets upon the Company’s liquidation, dissolution or winding up whether voluntarily or involuntarily.

Each of the Common Stock Offering and the Series B Offering is being made pursuant to the Company’s effective shelf registration statement on Form S-3 (Registration No. 333-201317), including the prospectus dated January 7, 2015 contained therein, as the same has been supplemented.

The sale of shares of Common Stock and Series B Convertible Preferred Stock is expected to close on February 11, 2015. Each Underwriting Agreement contains customary representations, warranties and agreements by the Company, customary conditions to closing, indemnification obligations of the Company and the Underwriter,

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including for liabilities under the Securities Act of 1933, as amended, other obligations of the parties and termination provisions. The representations, warranties and covenants contained in each Underwriting Agreement were made only for purposes of such agreement and as of specific dates, were solely for the benefit of the parties to such agreement and may be subject to limitations agreed upon by the contracting parties. Subject to certain exceptions, the Company and all of the Company’s directors and executive officers also agreed to not sell or transfer any common stock of the Company for 90 days after February 6, 2015 without first obtaining the consent of Jefferies LLC.

A copy of the Underwriting Agreement relating to the Common Stock Offering is attached hereto as Exhibit 1.1 and is incorporated herein by reference. A copy of the Underwriting Agreement relating to the Series B Offering is attached hereto as Exhibit 1.2 and is incorporated herein by reference. A form of the Certificate of Designation of Preferences, Rights and Limitations of Series B Convertible Preferred Stock is attached hereto as Exhibit 4.1 and is incorporated by reference herein. The foregoing description of the terms of the Underwriting Agreements and the rights, preferences and privileges of the Series B Convertible Preferred Stock is qualified in its entirety by reference to such exhibits. A copy of the opinion of Fenwick & West LLP relating to the legality of the issuance and sale of the securities in these offerings is attached as Exhibit 5.1 hereto.

Securities Exchange Agreement

On February 5, 2015, the Company and Biotechnology Value Fund, L.P. and Biotechnology Value Fund II, L.P. (collectively, “BVF”) entered into a Securities Exchange Agreement pursuant to which BVF exchanged an aggregate of 4,000,000 shares of the Company’s Common Stock for 4,000 shares of the Company’s Series B Convertible Preferred Stock (the “Exchange”). The Exchange is expected to close immediately prior to the closing of the Company’s Common Stock Offering and Series B Offering.

A copy of the Exchange Agreement is attached hereto as Exhibit 10.1 and is incorporated herein by reference. The foregoing description of the terms of the Exchange Agreement is qualified in its entirety by reference to such exhibit.

Item 8.01 Other Events.

On February 6, 2015, the Company issued a press release titled “Oncothyreon Prices $22 Million Concurrent Public Offerings of Common Stock and Preferred Stock.” A copy of the press release is filed as Exhibit 99.1 and incorporated herein by reference.

Item 9.01 Exhibits

Forward-Looking Statements

In order to provide the Company’s investors with an understanding of its current results and future prospects, this Current Report on Form 8-K contains statements that are forward-looking. Any statements contained in this press release that are not statements of historical fact may be deemed to be forward-looking statements. Words such as “believes,” “anticipates,” “plans,” “expects,” “will,” “intends,” “potential,” “possible” and similar expressions are intended to identify forward-looking statements. These forward-looking statements include the Company’s intention to conduct an offering of securities.

Forward-looking statements involve risks and uncertainties related to the Company’s business and the general economic environment, many of which are beyond its control. These risks, uncertainties and other factors could cause the Company’s actual results to differ materially from those projected in forward-looking statements, including the ability to manage successfully and complete the offering and exchange, the general economic and/or market conditions and the factors set forth in the Company’s filings with the Securities and Exchange Commission. Although the Company believes that the forward-looking statements contained herein are reasonable, it can give no assurance that its expectations are correct. All forward-looking statements are expressly qualified in their entirety by this cautionary statement. For a detailed description of the Company’s risks and uncertainties, you are encouraged to review the documents filed with the securities regulators in the United States on EDGAR and in Canada on SEDAR. The Company does not undertake any obligation to publicly update its forward-looking statements based on events or circumstances after the date hereof, except as required by applicable law.

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Date: February 6, 2015

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EXHIBIT INDEX

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